Port fuel direct injection (PFDI) engines include both port injection and direct injection of fuel and may advantageously utilize each injection mode. For example, at higher engine loads, fuel may be injected into the engine using direct fuel injection for improved engine performance (e.g., by increasing available torque and fuel economy). At lower engine loads and during engine starting, fuel may be injected into the engine using port fuel injection to provide improved fuel vaporization for enhanced mixing and to reduce engine emissions. Further, port fuel injection may provide an improvement in fuel economy over direct injection at lower engine loads. Further still, noise, vibration, and harshness (NVH) may be reduced when operating with port injection of fuel. In addition, both port injectors and direct injectors may be operated together under some conditions to leverage advantages of both types of fuel delivery or in some instances, differing fuels.
In PFDI engines, a lift pump (also termed, low pressure pump) supplies fuel from a fuel tank to both port fuel injectors and a direct injection fuel pump (also termed, a high pressure pump). The direct injection fuel pump may supply fuel at a higher pressure to direct injectors. During some engine conditions, e.g. lower engine loads, fuel may not be injected to the engine via direct injectors. As such, the direct injection fuel pump may be deactivated during these conditions. Specifically, a solenoid activated check valve at an inlet to a compression chamber of the direct injection fuel pump may be held in a pass-through mode allow fuel flow into and out of the compression chamber. A potential issue during such conditions is that the direct injection pump may degrade when fuel flow through the direct injection fuel pump is stopped. Specifically, the lubrication and cooling of the direct injection pump may be reduced while the direct injection pump is deactivated, leading to degradation of the direct injection pump.
One example approach for providing lubrication during deactivation of the direct injection fuel pump is shown by Pursifull et al. in US 2014/0224217. Herein, a pressure differential is produced in the direct injection fuel pump by controlling a pressure in the compression chamber during a compression stroke when fueling via direct injectors is disabled. Specifically, the pressure in the compression chamber during the compression stroke may be increased to a pressure higher than an output pressure of the lift pump. By increasing the pressure during the compression stroke, lubrication of a cylinder and pump piston of the direct injection fuel pump may be enhanced.
The inventors herein have identified a potential issue with the above approach. As an example, lubrication of the cylinder and pump piston of the direct injection fuel pump may not occur during a suction stroke in the direct injection fuel pump. Herein, the compression chamber may be at the same pressure as a step chamber (chamber formed underneath base of pump piston) and the lack of differential pressure may result in lubrication not occurring during at least a portion of each pump stroke. Without lubrication and cooling during the suction stroke, pump degradation may continue to be a problem.
The inventors herein have recognized the above issue and identified an approach to at least partially address the issue. The approach includes an example method comprising regulating a pressure in a step chamber of a direct injection fuel pump to a substantially constant pressure during each of a compression stroke and a suction stroke in the direct injection fuel pump. In this way, a differential pressure may be obtained in the direct injection fuel pump providing lubrication.
For example, a direct injection fuel pump coupled in an engine may include a pump piston reciprocating in a bore, the pump piston being driven by a crankshaft of the engine. A compression chamber may be formed on a first side of the pump piston and a step chamber may be formed on a second side of the pump piston wherein the first side and the second side are positioned opposite each other. In one example, the compression chamber is formed vertically above a top surface of the pump piston while the step chamber is formed vertically underneath the bottom surface of the pump piston. The step chamber may be fluidically coupled to an accumulator which stores fuel enabling a pressure of the step chamber to be regulated during each of a compression stroke and a suction stroke in the direct injection fuel pump. The accumulator may enable a substantially constant pressure in the step chamber with the constant pressure being higher than an output pressure of a lift pump.
In this way, lubrication of the direct injection fuel pump may be enabled during deactivation of direct injectors. By regulating pressure in the step chamber of the direct injection fuel pump, the bore and pump piston may be lubricated. Specifically, a pressure differential may be formed across the pump piston of the direct injection fuel pump that allows fuel to flow into a clearance between the pump piston and the bore providing lubrication. Accordingly, degradation of the direct injection fuel pump may be reduced allowing an improvement in the performance of the direct injection fuel pump. Further, the approach may be applied at lower cost and complexity. Furthermore, durability of the direct injection fuel pump may be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.